Silver is a metal that cannot be oxidized very well, is chemically fairly stable and has remarkable electrical properties. It is actually the most conductive metal that is known (ρ=1.57 μΩ·cm). This is why its use in the form of a thin film offers many advantages in the field of high critical temperature Tc superconductors and in microelectronics. For high Tc superconductors, it has been shown that a metal layer and in particular a silver layer placed directly above or below the superconductive material significantly improved the service life of the device, cable or tape. In the field of microelectronics and flat screens (TFT (=thin film transistors) technology), the silver can be used in connection in the electronic components by replacing the aluminum or copper currently used.
Various processes for obtaining a silver deposit on a substrate exist.
One process that consists in performing a flash evaporation of silver pivalate in solid form has been described by S. Samilenkov et al. (Chem. Vap. Deposition, 2002, 8, No. 2, 74). However, the temperature that is required for evaporating the pivalate is at least equal to the decomposition temperature, which generates product losses and a poor yield.
Other compounds have been used for making Ag deposits by CVD. Thus, the use of (1,1,1,5,5,5-hexafluoro-2,4-pentanedionato) silver [bis-(trimethylsilyl)acetylene complexes has been described by Chi, Kai-Ming, et al. [Chem. Vap. Deposition (2001), 7, No. 3, 117-120]. The use of silver precursors of fluorinated β-dicetonate type for depositing silver films by CVD was described in particular in JP-08053470. U.S. Pat. No. 5,096,737 describes precursors for the deposition by CVD of films of various metals on a substrate. The precursors are of the (COD)M(I) (hfacac) type, whereby M is Cu, Ag, Rh, or Ir. However, in all of these processes, the use of fluorinated precursors runs the risk of introducing fluorine into the deposited silver layers.
Processes that use precursor solutions have been described in particular by J. P. Sénateur et al. (“Pulsed Injection MOCVD of Functional Electronic Oxides,” Adv. Mater. Opt. Electron, 10, 155, 2000) and by H. Guillon et al. (“Injection MOCVD, Historical and State of the Art,” Multimetox Network Newsletter, Issue 4, November 2001, p. 3). These techniques, however, can only be used for depositions of metals for which soluble precursors exist in solvents that can be used in CVD. The non-fluorinated silver complexes that are described in the prior art are then generally not very soluble in such solvents.